Method and device for diagnosing trouble with sensor function

ABSTRACT

A sensor for converting a physical quantity into an electric signal and issuing the output is driven by a drive circuit which is driven by a drive signal issued from a 1-chip microcomputer. The 1-chip microcomputer judges fault of sensor function when the sensor output signal is out of a specified output range. Further, when stopping the operation of the drive circuit, if the sensor output signal does not coincide with a specific value, the 1-chip microcomputer also judges fault of sensor function. According to the invention, in the event of a trouble of sensor function allowing the sensor output signal to settle within an output range, such trouble can be detected.

TECHNICAL FIELD

The present invention relates to a fault diagnosis method and device ofsensor function in an apparatus for output control with a 1-chipmicrocomputer into which an electric signal issued from a sensor forconverting a physical quantity into an electric signal is fed.

BACKGROUND ART

A conventional example of fault diagnosis system of sensor function isexplained by referring to FIG. 7. An output signal S1 from a drivecircuit 1 is input into a sensor 2, and the sensor 2 is driven. Thesensor 2 converts a physical quantity into an electric signal, and sendsout a sensor output signal S2. The sensor output signal S2 is input intoan interface circuit 3. The interface circuit 3 processes the sensoroutput signal S2 into a signal to be recognized by a 1-chipmicrocomputer 4, and issues an electric signal (digital signal) S3.

The 1-chip microcomputer 4 converts the electric signal S3 received fromthe interface circuit 3 into a control signal S4 having a specifiedfunction by a program stored in a memory 4A in advance, and issues to anoutput circuit 5. The output circuit 5 drives a load 6 depending on thedrive signal S4.

The sensor output signal S2 usually settles within a certain outputrange of the sensor output. However, it a function trouble occurs in thesensor 2, and the sensor output signal S2 does not settle within theoutput range, the electric signal S3 from the interface circuit 3 goesout of the input range of the 1-chip microcomputer 4. Accordingly, the1-chip microcomputer 4 issues a fail signal S5. When receiving the failsignal S5, the output circuit 5 lights up a fail lamp 7. As a result, ifthe sensor output signal S2 does not settle within the output range,such trouble of the sensor function can be detected.

However, in spite of the trouble in the sensor function, if the sensoroutput signal S2 settles within the output range, it is not known whatsignal is produced when the electric signal S3 is issued from theinterface circuit 3, and it is hard to detect fault of the sensorfunction.

It is hence an object of the invention to present a method and devicefor fault diagnosis of sensor function capable of detecting trouble ofsensor function even if a sensor output signal issued from a sensorsettles within a certain output range.

DISCLOSURE OF INVENTION

In order to achieve the object, the invention is characterized in afault diagnosis method of sensor function in an apparatus forcontrolling an output by using a 1-chip microcomputer which receives anelectric signal from a sensor for converting a physical quantity intothe electric signal, wherein a drive circuit for driving the sensor isdriven by a drive signal issued from the 1-chip microcomputer.

The invention is also characterized in that a fault diagnosis device ofsensor function in an output control apparatus including a sensor forconverting a physical quantity into an electric signal and issuing, anda 1-chip microcomputer for controlling the output by receiving theelectric signal, comprises a drive circuit for driving the sensor, asbeing controlled by a control signal issued from the 1-chipmicrocomputer, wherein the 1-chip microcomputer diagnoses the fault ofsensor function by controlling an operation of the drive circuit.

According to the invention, it is possible to detect trouble of sensorfunction even if the sensor output range settles within an output range.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a fault diagnosis system of sensorfunction in an embodiment of the invention;

FIG. 2 is a flowchart showing an outline of operation of 1-chipmicrocomputer;

FIG. 3 is a block diagram showing a fault diagnosis system of a slantsensor in a specific example of the invention;

FIG. 4A to FIG. 4C are diagrams showing the relation between theelectrode of the slant sensor and liquid level of dielectric solution;

FIG. 5 is an output voltage characteristic diagram corresponding to theangle of the slant sensor in FIG. 3;

FIG. 6 is an output voltage characteristic diagram corresponding to theangle of the slant sensor in FIG. 3, showing the frequency dependence;and

FIG. 7 is a block diagram showing a fault diagnosis system of sensorfunction in a prior art.

BEST MODE FOR EMBODYING THE INVENTION

Referring now to the drawings, the invention is specifically describedbelow. FIG. 1 is a block diagram of a fault diagnosis system of sensorfunction in an embodiment of the invention.

In the drawing, a 1-chip microcomputer 14 issues a drive signal S16 (forexample, a clock signal) according to a program stored in a memory 14Ain advance, and the drive signal S16 is input into a drive circuit 11.An output signal S11 from the drive circuit 11 is input into a sensor12, and the sensor 12 is driven. The sensor 12 converts the physicalquantity into an electric signal, and issues a sensor output signal S12.The sensor output signal S12 is input into an interface circuit 13. Theinterface circuit 13 processes the sensor output signal 12 into a signalto be recognized in the 1-chip microcomputer 14, and an electric signal(digital signal) S13 is issued.

The 1-chip microcomputer 14 converts the electric signal S13 receivedfrom the interface circuit 13 into a control signal S14 having aspecified function by the program stored in the memory 14A, and issuesto an output circuit 15. The output circuit 15 drives a load 16depending on the control signal S14.

When the 1-chip microcomputer 14 stops the drive circuit 11 by the drivesignal S16, the sensor 12 issues a predetermined specific sensor outputsignal S12. The interface circuit 13, receiving the specific sensoroutput signal S12, issues a corresponding specific electric signal(digital signal) S13.

Suppose, in spite of trouble in the sensor 12, a sensor output signalS12 within a certain output range is being issued from the sensor 12. Inthis case, when the drive circuit 11 is stopped by stopping the drivesignal S16 from the 1-chip microcomputer 14, the predetermined specificsensor output signal S12 is not issued from the sensor 12, and then thespecific sensor output signal S13 is not issued from the interfacecircuit 13. As a result, the 1-chip microcomputer 14 judges that thesensor 12 is defective, and issues a fail signal S15 to the outputcircuit 15. Consequently, the output circuit 15 lights up a fail lamp17.

Due to trouble in the sensor 12, meanwhile, if the sensor output signalS12 does not settle within the output range, the electric signal S13from the interface circuit 13 goes out of the input range of the 1-chipmicrocomputer 14. Accordingly, the 1-chip microcomputer 14 issues a failsignal S15 to light up the tail lamp 17, thereby realizing faultdiagnosis, which is same as in the prior art.

FIG. 2 is a flowchart explaining the operation of the 1-chipmicrocomputer 14. At step S1, fault diagnosis mode is judged, and ifjudged negatively (execution mode), going to step S2, the drive circuit11 is driven. At step S3, the electric signal S13 from the interfacecircuit 13 is judged to be within specified output range or not. Ifjudged affirmatively, going to step S4, the sensor 12 is judged to benormal. At step S5, the load 16 is driven, and at step S6, it is judgedif the drive terminating command of the sensor 12 is received or not. Ifjudged affirmatively, the operation is terminated, but if judgednegatively, the process returns to step S1. Thus, in normal operation,steps S1 to S6 are repeated, but if judged negatively at step S3, the1-chip microcomputer 14 judges that the sensor 12 has a functiontrouble, and goes to step S12 to light up the fail lamp 17.

If judged affirmatively at step S1 to get into fault diagnosis mode,going to step S8, the 1-chip microcomputer 14 stops the operation of thedrive circuit 11. At step S9, it is judged if the electric signal S13from the interface circuit 13 is a predetermined specific value or not,and if judged affirmatively, the process goes to step S10, and thesensor 12 is judged to be normal. If judged negatively at step S9, goingto step S11, the sensor 12 is judged to be abnormal. The process goes tostep S12 and the fail lamp 17 is lit up.

In this manner, the 1-chip microcomputer 14 detects failure of thesensor 12.

A specific example of the invention is described. FIG. 3 is a blockdiagram of a device for output control using a slant sensor fordetecting the inclination of liquid level of dielectric solution aschange in the electrostatic capacity, in which the inclination angle ofthe slant sensor controlled by the drive signal issued from a 1-chipmicrocomputer is converted into an electric signal, and this electricsignal is input into the 1-chip microcomputer.

The 1-chip microcomputer 24 generates a clock signal S26 by a programstored in a memory 24A in advance, and supplies the clock signal S26into a buffer circuit (for example, C-MOS inverter) 21 as a drivecircuit. The buffer circuit 21 shapes the waveform of the clock signalS26, and corrects, for example, dullness of the waveform. The shapedclock signal S21 is supplied into a slant sensor 22.

The slant sensor 22 detects the inclination of the dielectric solutionas a change in the electrostatic capacity. The slant sensor 22 iscomposed of electrostatic capacities 22C, 22D changing depending on theinclination, and C-V (capacity-voltage) converters 22A, 22B forconverting the two electrostatic capacities into voltages, and outputvoltages V1, V2 are respectively produced from the C-V converters 22A,22B. In this manner, the inclination angle is converted into (V2−V1).The principle and structure of the slant sensor 22 are known, and areexplained only briefly herein.

FIG. 4A, FIG. 4B, and FIG. 4C are schematic diagrams of the slant sensor22 and inclination θ. The slant sensor 22 comprises a common electrode30, semicircular first electrode 31 a and second electrode 31 b havingthe both ends cut off, and a dielectric solution 34 contained in thespace formed by the common electrode 30 and first and second electrodes31 a, 31 b. The common electrode 30 and first and second electrodes 31a, 31 b are disposed parallel to each other at specific intervals.

At the inclination θ=0, as shown in FIG. 4A, the liquid level 34 a ofthe dielectric solution 34 does not reach the first electrode 31 a,while the second electrode 31 b is completely immersed. Accordingly, thedifference between the electrostatic capacity C1 of the first electrode31 a and the electrostatic capacity C2 of the second electrode 31 b isthe largest, and the absolute value of (V2−V1) is the maximum. Next, atθ>0 or θ<0, as shown in FIG. 4B and FIG. 4C, respectively, the absolutevalue of the difference of the electrostatic capacity C1 of the firstelectrode 31 a and the electrostatic capacity C2 of the second electrode31 b decreases as the value of θ increases in the positive or negativedirection.

On the other hand, as the inclination θ increases in the positive ornegative direction, the absolute value of (V2−V1) decreases according toa quadratic function.

An amplifier circuit 23 as the interface circuit is composed of twooperational amplifiers 23A, 23B, a reference voltage (Vref) 23C, andresistances 23D to 23G (R1 to R4), and output voltages V1, V2 of theslant sensor 22 are fed into the operational amplifiers 23A, 23B,respectively. The output signal S23 of the amplifier circuit 23 isexpressed in the following formula (1).S 23=−[(R 1+1)/R 2]×|V 2−V 1|+Vref  (1)where R1=R2 and R2=R3.

Herein, the output signal S23 is adjusted and issued as a gain that canbe recognized by the 1-chip microcomputer 24 according to the ratio ofR1 and R2. For example, it is set in a voltage range of 1 V to 4 V. Theabsolute value of (V2−V1) changes according to a quadratic function.

The 1-chip microcomputer 24 recognizes the inclination angle by puttingthe output signal S23 in the program stored in the memory 24A in advanceand issues an output signal S24 to the output circuit 25. The outputcircuit 25 drivers the load 26 depending on the output signal S24.

The output signal S23 is set so as to be issued within a certain voltagerange (for example, 1 V to 4 V). If the slant sensor 22 issues abnormalvoltages V1, V2 and the output voltage of the output signal S23 is outof the preset voltage range, the 1-chip microcomputer 24 judges that theslant sensor 22 is defective by the program stored in the memory 24A. Asa result, a fail signal S25 is issued, and the fail lamp 27 is lit upthrough the output circuit 25.

While the slant sensor 22 is driven by the clock signal S21, when theclock signal S21 is stopped (fixed at H or L), the output voltage(V1−V2) of the slant sensor 22 becomes 0 V, and the output signal S23becomes S23=Vref according to formula (1). That is, while the slantsensor 22 is normal, if the clock signal S21 is stopped, a specificvoltage Vref is input into the 1-chip microcomputer 24.

In other words, if the voltage of the output signal S23 when the 1-chipmicrocomputer 24 stops the clock signal S26 is an expected value ofVref, the sensor function is normal, and if not expected value, that is,other voltage than Vref, the sensor function is abnormal, and trouble isjudged.

The sensitivity of the slant sensor for detecting the inclination of thedielectric solution as the change in the electrostatic capacity dependson the clock frequency. Accordingly, in other method of fault diagnosis,by varying the frequency without stopping the clock, the sensitivity ofthe slant sensor is changed, and an expected value may be obtained.

FIG. 5 is a diagram showing the output voltage corresponding to atypical angle when the output of the slant sensor for detecting theinclination of the dielectric solution as the change in theelectrostatic capacity is amplified in a differential amplifier circuit.In the diagram, line (a) shows the characteristic when the 1-chipmicrocomputer 24 stops sending of clock signal S21 (fault diagnosismode), and curve (b) shows the characteristic when the 1-chipmicrocomputer 24 is sending out the clock signal S21 (execution mode).As shown in the diagram, in the execution mode, if the inclination angleθ=0, the output voltage is the lowest, and as the inclination angle θincreases in the positive or negative direction, it increases accordingto a quadratic function.

FIG. 6 is a diagram showing the frequency dependence when the output ofthe slant sensor for detecting the inclination of the dielectricsolution as the change in the electrostatic capacity is amplified in adifferential amplifier circuit. As shown in the diagram, as the clockfrequency becomes lower, the characteristic of the output voltage isshifted upward.

Industrial Applicability

As described herein, according to the invention, the sensor function canbe checked by the program stored in the 1-chip microcomputer in advance,and early fault diagnosis of sensor function and fault notice to outsideare realized, and malfunction is prevented and safety is enhanced.

The invention is not limited to the illustrated embodiment alone, butmay be changed and modified in various forms according to the principleof the invention, and hence these changes and modifications are alsoincluded in the scope of the invention.

According to the invention, since the sensor function can be checked bythe program stored in the 1-chip microcomputer in advance, early faultdiagnosis of sensor function and fault notice to outside are realized.

1. A fault diagnosis method for diagnosing a sensor function in anapparatus for controlling an output by using a 1-chip microcomputerwhich receives an electric signal from a sensor for converting aphysical quantity into the electric signal, comprising the steps of:driving a drive circuit for driving the sensor with a drive signalissued from the 1-chip microcomputer; said 1-chip microcomputerreceiving an electric signal on the basis of the sensor during normaloperation by issuing the drive signal, and receiving an electric signalon the basis of the sensor at a predetermined specific value duringstopping of the drive signal; and diagnosing a fault of the sensorfunction when the electric signal of the predetermined specific value isnot received during stopping of the drive signal, thereby detecting afault of a sensor function even if the sensor output settles within anoutput range of the sensor.
 2. The fault diagnosis method for diagnosinga sensor function of claim 1, wherein said 1-chip microcomputer has aprogram stored in advance, and executes fault diagnosis of the sensorfunction.
 3. A fault diagnosis method for diagnosing a fault of a sensorfunction in an apparatus for controlling an output by using a 1-chipmicrocomputer, comprising the steps of: receiving an electric signalfrom a sensor for converting a physical quantity into the electricsignal; driving a drive circuit for driving the sensor with a drivesignal issued from the 1-chip microcomputer; said 1-chip microcomputerreceiving the electric signal on the basis of the sensor during normaloperation by issuing the drive signal, and receiving the electric signalwith an expected characteristic from the sensor by varying a frequencyof the drive signal; and diagnosing the fault of the sensor functionwhen the electric signal with the expected characteristic is notreceived during varying of the frequency of the drive signal, therebydetecting a fault of a sensor function even if the sensor output settleswithin an output range of the sensor.
 4. The fault diagnosis method fordiagnosing a fault of a sensor function of claim 3, wherein said 1-chipmicrocomputer has a program stored in advance, and executes faultdiagnosis of the sensor function.
 5. A fault diagnosis device fordiagnosing a fault of a sensor function in an output control apparatus,comprising: a sensor for converting a physical quantity into an electricsignal; a 1-chip microcomputer for controlling an output upon receivingthe electric signal; and a drive circuit controlled by a control signalissued from the 1-chip microcomputer to drive the sensor, wherein said1-chip microcomputer stops driving of the drive circuit and detectswhether the sensor is outputting a specific value as a basis to diagnosethe fault of the sensor function, thereby detecting a fault of a sensorfunction even if the sensor output settles within an output range of thesensor.
 6. The fault diagnosis device for diagnosing a fault of a sensorfunction of claim 5, wherein the drive circuit comprises a buffercircuit for shaping a waveform of the signal from the 1-chipmicrocomputer.
 7. The fault diagnosis device for diagnosing a fault of asensor function of claim 5, further comprising: an interface circuit foramplifying the signal from the sensor and then sending it to the 1-chipmicrocomputer.
 8. A fault diagnosis device for diagnosing a fault of asensor function in an output control apparatus, comprising: a sensor forconverting a physical quantity into an electric signal; a 1-chipmicrocomputer for controlling an output by receiving the electricsignal; and a drive circuit for driving the sensor being controlled by acontrol signal issued from the 1-chip microcomputer, wherein said 1-chipmicrocomputer changes a frequency of the drive signal supplied to thedrive circuit and detects whether the sensor output is the electricsignal with an expected characteristic, thereby diagnosing the fault ofthe sensor function, thereby detecting a fault of a sensor function evenif the sensor output settles within an output range of the sensor. 9.The fault diagnosis device for diagnosing a fault of a sensor functionof claim 8, wherein the drive circuit comprises a buffer circuit forshaping a waveform of the signal from the 1-chip microcomputer.
 10. Thefault diagnosis device for diagnosing a fault of a sensor function ofclaim 8, further composing: an interface circuit for amplifying thesignal from the sensor and then sending it to the 1-chip microcomputer.